Muffling tubes



p 1962 M. APPLEGATE 3,054,474

MUFFLING TUBES Filed June 2, 1958 INVENTOR United States This inventionis related to that of my Patent Number 2,805,730, issued Sept. 10, 1957.

The principal object of this invention is the production of a flexibletube combining the characteristics of an exhaust tube andsound-absorbent mufller for internal combustion engines. Another objectis to produce such a tube in economical form which can be manufacturedwith a minimum number of parts in machinery of conventional design.Still .another object is a mufiiing tube which has a favorable internaldiameter relative to external diameter consistent with good performance.Another object is to utilize the sound-absorbent characteristics ofmaterials as effectively as possible within the limitations of overalldimensions. An object of the invention also is to achieve a favorablerelationship of material and construction costs to muflling performancein a flexible tube. Another object is to produce a tube which permitsflexibility in the dimensions of the components for the most effectiveinternal configuration and the most economically effective relationshipof dimensions, configuration and properties of sound-absorbentmaterials. And, still another object is to combine different materialsin arrangements favorable to economical continuous manufacture,effective sound absorption and length of useful life in service.

What constitutes this invention is set forth in the specificationfollowing with reference to the accompanying drawing and is succinctlydefined in the appended claims.

In the drawing, FIGURE 1 is a schematic side View, not to scale, partlysectional, showing the essential components of my invention in anenlarged diagrammatic form.

My invention is composed of four parts, 1, a metal strip formed androlled spirally into a conventional flexible metal tube, two strips, 2and 3 of sound-absorbent material such as woven glass fiber or asbestosand a metal strip 4. Strips 2, 3 and 4 are interleaved and woundspirally along with strip 1 to be held between the overlapping edges 5and 6 of strip 1, and formed so the inner edges 7, 8, and 9 of strips 2,3 and 4 respectively protrude into the interior of the tube.

The principal purpose of metal strip 4 is to hold the inner edges 7 and8 of fibrous strips 2 and 3 radially into the interior of the tube. Alsoin my present invention, two sound-absorbent strips 2 and 3, one on eachside of the metal strip 4, increase the sound-absorbent ability of thetube to attain results which cannot so readily be accomplished with asingle strip of soundabsorbent material.

Strip 4, being formed with a considerable portion of width rolledradially and projecting into the interior of the tube is preferably ofmetal easily formed into an edge-wound spiral. Some wrinkling of theinner edge 9 of strip 4 is to be expected but this is not .animpairment.

Strip 2 will not always remain close to strip 4 as shown in the drawingbut may tend to assume a different configuration. The sound-absorbenteffect of strip 2 in either case is effective.

A modification of FIGURE 1 of my present invention for economy isaccomplished by omitting either strip 2 or strip 3 and retaining onlyone sound-absorbent strip along with metal strip 4. Either arrangementwould be effective, the choice being a matter of design.

atent In the operation of my present invention it is sometimes desirableto take account of the direction of flow of gas through the tube. Forexample, it may be desirable to utilize the baflling effect of theinward projecting surface of strip 4 to protect strip 3 from the directimpact of gas flow, or conversely to protect strip 2 in the otherdirection.

If strip 2 occupies a position as shown in the drawing but without strip3, and the flow of gas is oriented to impinge on strip 4 in advance ofstrip 2, the baffling and heat-absorbing ability of strip 4 will protectstrip 2 from all but turbulent contact of gas on strip 2, and strip 2will be required only to absorb sound energy with a minimum of erosionthereon from the moving gas.

The mechanical processes of manufacture of flexible tubes withinterleaved fibrous strips are known in the art wherein a paper strip issometimes combined with a flexible steel tube to produce a paper-linedflexible tube for carrying wires in electrical work. There has beeninvented, also, a flexible tube with an interwound metallic stripintended for use .as a mufliing tube. Thus the mechanical technology forthe construction of my invention has already in part been developed.

My invention is distinguished from the most nearly comparable prior artin that I use one or two strips, 2 and 3, of fibrous material forabsorbing sound energy together with a metal strip, 4, for positioningand protecting the sound-absorbent strip. The prior art showing only ametal strip depends primarily upon turbulence as distinguished from acombination of turbulence and direct sound absorption as accomplished inmy present invention.

The acoustic principles of the use of sound-absorbent fibrous materialsand the desirability of using materials such as asbestos or fiber glasshave been set forth in my issued patent referred to above. Theadvantages of flexible tubing for muffling and the advantage of aminimum of baffling in muflling systems also have been presented in theabove mentioned patent. My present in vention has, in common with myother invention the advantages of compactness, minimum baffling, and theeffective use of sound-absorbent materials. The soundabsorbent strips 2and 3 in my present invention should for this use be combustionresistant. Permeability and a large effective fiber area are desirablefor maximum effect of sound absorption.

In determining the dimensions in my invention it will be observed thatthe ordinary mufiler is usually only about two or three feet long, butthat the total length of exhaust pipe and muffler is usually ten feet ormore. The muffling effect per foot of tube as made in this invention canbe about one-fourth of that of a conventional muflier and still, byvirtue of employing a length of mufller tubing equal to that of theusual exhaust pipe and mufller be as efiiective as the conventionalmufller. An internal diameter of one and one-half to two inches in tube1 for example, and moderate internal extension of strips 2, 3 and 4allow a structure that is economical, reasonably compact, and effectivefor conventional vehicles.

I claim:

1. A flexible tube formed of an overlapping continuous metal strip,wound and interleaved with a plurality of continuous strips of fibrousmaterial and a second continuous strip of metal paralleling said fibrousstrip, said strips of fibrous material and said second strip of metalbeing formed to project into the interior of the formed tube.

2. A flexible tube formed of a continuous metal strip with overlappingedges, two fibrous strips and a second metal strip, said fibrous andsecond metal strips interlocked between the overlapping edges of thefirst said 3 metal strip, and projecting radially into the interior ofthe formed tube.

3. A spirally wound mufliing tube formed of a resilient flexible stripformed with overlapping edges, a plurality of resilient flexiblesound-absorbent strips interlocked therein, and a metal stripparalleling said sound-absorbent strip also interlocked therein, saidsound-absorbent strip and said paralleling metal strip projecting intothe interior of the wound tube.

4. A mutfling tube comprising a spirally wound strip with overlappingedges, a plurality of strips of fibrous sound-absorbent materialinterlocked therein and project ing inwardly toward the center of saidtube, and a metal strip paralleling said fibrous strips and interlockedtherewith, also projecting inwardly toward the center of the tube.

5. A muflling tube comprising a spirally wound strip with overlappingedges, two strips of sound-absorbent material and a strip of metalparalleling said soundabsorbent strips and interlocked between saidoverlapping edges, and projecting into the interior of the wound tube.

6. A mufiiing tube comprising a spirally Wound strip with overlappingedges, two strips of sound-absorbent material and a strip of metalbetween them, the three strips being interlocked between saidoverlapping edges, and projecting into the interior of the wound tube.

7. A muffling tube comprising a spirally wound strip with overlappingedges, two strips of sound-absorbent material and a strip of metalbetween them, the three strips being interlocked between said edges andprojecting radially inside the resultant tube.

8. A mufiling tube comprising a spirally wound strip with interlockingedges, twostrips of sound-absorbent material and a strip of metalbetween them, the three strips being interlocked between said edges andprojecting substantially radially into the interior of the resultanttube.

9. A muflling tube comprising a spirally wound strip with interlockingedges, two strips of sound-absorbent 4- material and a strip of metalbetween them, the three strips being interlocked between said edges, andprojecting into the interior of the resultant tube, the metal and onefibrous strip projecting approximately radially toward the center ofsaid tube.

10. A flexible tube comprising a spirally wound strip with over-lappingedges, a metal strip and a plurality of fibrous strips retained betweensaid overlapping edges, and formed so they project inwardly into theresultant tube.

11. A flexible tube comprising a spirally wound strip with overlappingedges, a metal strip and two fibrous strips each retained over part oftheir width between said overlapping edges, and formed so part of thewidth of said metal and fibrous strips project inwardly into theresultant tube.

12. A flexible tube comprising a spirally wound strip with overlappingedges, a metal strip and two fibrous strips each retained over part oftheir width between said overlapping edges, and formed so they projectat the unretained edges for a portion of their width into the interiorof the resultant tube.

13. A flexible tube comprising a spirally wound strip with overlappingedges, a metal strip and at least one fibrous strip, each retained overtheir edges and part of their respective widths between said overlappingedges, and formed so their other edges and a portion of their widthsproject into the interior of the resultant tube.

References Cited in the file of this patent UNITED STATES PATENTS1,015,698 Maxim Jan. 23, 1912 1,115,873 Spencer Nov. 3, 1914 1,530,324Pribil Mar. 17, 192.5 1,909,511 Wilson May 16, 1933 2,014,368 BlundellSept. 17, 1935 2,718,273 Deh us Sept. 20, 1955 2,805,730 Applegate Sept.10, 1957

